Paper I — 2022 February (2019 Scheme) — Q9

Paper I

2022 February (2019 Scheme) · 100 marks · 180 min

Question

Laboratory diagnosis of acute promyelocytic leukemia.

Q94 marksShort Answers★✓

Answer

Acute promyelocytic leukaemia (APL) is a distinct subtype of AML (AML-M3 in the older FAB classification).

Peripheral blood/bone marrow morphology

• Abnormal promyelocytes with heavy azurophilic granulation
• Bundles of Auer rods in the cytoplasm (“faggot cells”) — characteristic finding
• Bilobed/reniform nuclei

Cytogenetics

• Characteristic reciprocal translocation t(15;17)(q22;q12), fusing the PML gene (chromosome 15) with the RARA (retinoic acid receptor alpha) gene (chromosome 17), producing the PML-RARA fusion protein — confirmed by FISH or RT-PCR

Immunophenotyping (flow cytometry)

• Positive for myeloid markers (CD13, CD33, MPO)
• Characteristically negative or dim for HLA-DR and CD34 (helps distinguish from other AML subtypes)

Coagulation studies

• Screening for disseminated intravascular coagulation (DIC) — a critical and often presenting complication of APL: prolonged PT/aPTT, low fibrinogen, elevated D-dimer/fibrin degradation products, thrombocytopenia

Clinical significance

• Prompt recognition is essential because APL is uniquely sensitive to all-trans retinoic acid (ATRA), which induces differentiation of the malignant promyelocytes, and because of the high risk of fatal haemorrhage from DIC if treatment is delayed

Related Concepts

1. 1Acute Leukaemia

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